A data bus protocol adapted for controlling devices on a data bus between a host processing platform and a bit map printer for effectively transferring image data between the various image handling devices, the protocol comprising command instructions from a bus controller to the devices for specifying the data transfer path and timing, and transfer instructions for initiating the actual transfer.
A printing system may consist of nothing more than an off-the-shelf terminal and a bit map printer, but the printing speed will be low because some functions, such as compression, decompression, scaling, rotation and character generation are performed slowly in software A standard way of speeding up this kind of process is to do the most time-consuming processes in hardware, typically in ASICs, devices specially designed for the process, which run considerably faster than the equivalent software. These could be mounted on an additional board in the terminal but the terminal data bus does not have the bandwidth to handle these image handling processes at high printer speeds. Special purpose printer controllers could be built, but they are more expensive than the equivalent commercial terminals. Thus, there would be a significant cost benefit if commercial terminals could be adapted to high speed image printing.